More Links: Good article, video, tool, problems, game, and activity

What I've stumbled upon in the past two days:

• Can't keep up with the good articles I'd like to read. The De Morgan Forum pointed me to an article by Liping Ma, whose writing always gets me thinking. 
• Malke's love for the math found in stars primed me to take notice of this video by Toomai on stellations. He notices something intriguing that I'd like to explore when I have more time...
•  I think some day I'll want to explore the tools available at SageMath.

And some older ones (as I begin to slowly clear out my backlog...):

• Megan's thoughts on ranking tasks as a way to get students to grapple with definitions. Hmm, I wonder if I could design a good activity for my calculus or linear algebra courses.
• The link takes you to an illustration of adding cubes, but the page that's on is a huge collection of good problems.
• Kate's logic game, whose name has not been decided, looks great. I'd use it in Discrete Math. Reminds me of an old game called WFF 'n Proof.
• On inventing number systems (with third graders).